Determination of tensile strength perpendicular to the fibers of wooden materials reinforced with basalt, glass fiber-reinforced polymer, and plaster mesh

Karaman, A., Yeşil, H., and Yazıcı, H. (2025). "Determination of tensile strength perpendicular to the fibers of wooden materials reinforced with basalt, glass fiber-reinforced polymer, and plaster mesh," BioResources 20(1), 42–56.

Abstract

Wood is a heterogeneous and anisotropic material, and its mechanical properties are different from other building materials. It is necessary to know the mechanical properties of wood materials in buildings, such as carriers, floor beams, roof timber, plywood roof covers, laminated beams, stair or wire poles, yacht poles, and furniture frames. Tensile strength is the resistance of wood material to two forces applied in opposite directions, trying to break and separate the fibers. This study aimed to determine the tension strength perpendicular to fibers of beech timber reinforced with basalt fiber-reinforced polymer (BFRP), glass fiber-reinforced polymer (GFRP), and plaster mesh (PSM). One component polyurethane (PUR-D4) and polyvinyl acetate (PVAc-D4) were used as the adhesive. The BFRP, GFRP, and PSM were added as one layer of reinforced materials. Experimental materials reinforced with BFRP, GFRP, and PSM were tested in the unreinforced locations, of reinforced lumber with BFRP, GFRP, and PSM. Tests were performed to investigate the tensile strength perpendicular to fiber (┴σt). The test results showed that the reinforcement process increased the (┴σ). The ┴σt value of samples reinforced with BFRP was 13%, 32%, and 66% higher than those reinforced with GFRP, unreinforced, and reinforced PSM, respectively. Accordingly, the BFRP shows potential to serve as an option for reinforced wood structural members.

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Determination of Tensile Strength Perpendicular to the Fibers of Wooden Materials Reinforced with Basalt, Glass Fiber-Reinforced Polymer, and Plaster Mesh

Abdurrahman Karaman,^a,* Hüseyin Yeşil,^b and Hikmet Yazıcı ^c

DOI: 10.15376/biores.20.1.42-56

Keywords: BFRP; GFRP; PSM; PVAc-D4; PUR-D4

Contact information: a: Department of Forestry, Banaz Vocational School, Uşak University, 64500 Banaz/Uşak, Turkey; b: Department of Design, Simav Vocational School, Kütahya Dumlupınar University, 43500 Simav/Kütahya, Turkey; c: Department of Design, Çaycuma Vocational School, Zonguldak Bülent Ecevit University, 67900 Çaycuma/Zonguldak, Turkey;

* Corresponding author: abdurrahman.karaman@usak.edu.tr

INTRODUCTION

As an environmentally friendly, sustainable resource, lumber is a renewable material that is commonly used for structural components, building constructions, and a wide range of other applications involving engineered wood. However, the organic nature of lumber means that its mechanical properties may deteriorate throughout its life cycle. Biological degradation (insects, fungi, bacteria), natural defects (knots, deviation, grain, etc.), and environmental conditions can also greatly affect mechanical properties and reduce the tensile strength by up to 90% (Thelandersson and Larsen 2003).

The quality of adhesion in glues depends on the fluidity of the glues, which have desired properties such as penetrating both surfaces of the wood material, distributing homogeneously on the applied surface, forming layers, and wetting the surfaces (Vıck 1999). The effectiveness of glue is expected to depend on its viscosity, molecular weight, surface penetration, amount of solid matter, pH ratio, and application method; the adhesion results also will depend on the wood material, type, density, surface roughness and cleanliness (Rowell 2005). The heterogeneous distribution of the glue on the surface where it is applied negatively affects the cohesion and causes the wood material joints to open (Smardzevski 2002). During the processing of wood material, roughness on the surfaces due to the wood structure negatively affects adhesion (Efe and Gürleyen 2007). Sanded surfaces generally show more effective adhesion than planed surfaces in wood materials (Caster et al. 1985). A strong adhesion is achieved by properly processing the wood surface with cutters, applying the adhesive evenly over the entire surface, and cold pressing the wooden elements closed together (Selbo 1975). When sufficient pressure is applied to bond smooth-surfaced parts, the transfer of glue from one surface to another becomes uniform and the adhesion resistance gives the best results. When 0.7 N/mm² pressure is applied when joining perfect surfaces, adhesion resistance reaches the highest value (Franklin Glue Company 1989).

Fiber-reinforced polymers can exhibit several advantageous properties, including high mechanical strength, non-conductive lightweight composition, reduced recycling requirements, and corrosion resistance. The FRP has been employed for decades to enhance the structural integrity and augment the structural strength of concrete structures (Jiang et al. 2019). FRP has been used in bridge coatings, I-beam manufacturing, wooden beams and columns, restoration applications, and all types of strengthening, reinforcing joints due to its strength properties (Schober et al. 2015). Structural composite lumber may be reinforced with synthetic fibers to effectively improve its structural properties (Brol and Wdowiak-Postulak 2019). Additionally, FRP strengthening can enhance the bending stiffness and the ultimate bearing capacity of wood beams. Currently, various types of FRPs are available for structural reinforcement, including BFRP (Basalt FRP), GFRP (Glass FRP), AFRP (Aramid FRP), and CFRP (Carbon FRP) (Jian et al. 2022).

Many studies have investigated the mechanical properties of wooden structures reinforced with FRP materials. André and Johnsson (2010) investigated the use of GFRP and flax fiber composites to reinforce glue-laminated (glulam) timber samples to achieve tensile strength perpendicular to the fibers and more ductile fracture. Speranzini et al. (2010) conducted a four-point bending test on timber beams externally reinforced with hemp, glass, carbon, basalt, and flax FRP. Borri et al. (2013) investigated the strengthening of low-grade and high-grade wood beams using flax and BFRP. de la Rosa García et al. (2013) studied data obtained experimentally using bending tests of pine timber beams reinforced with composite materials. Osmannezhad et al. (2014) investigated the bending strength of the specially reinforced glulams with the GFRP. Schober et al. (2015) explained the potential applications of FRP for the reinforcement of timber structures. de la Rosa García et al. (2016) studied the increase in stiffness experienced on pine timber beams when reinforced with composite fabrics. The CRFP and BFRP fabrics of different weights were applied, and placed in a “U” shape, wrapping part of the beam section. Basterra et al. (2017) studied the flexural behavior of Populus euroamericana I-214 low-grade glulam timber beams, internally reinforced with the GFRP. Wang et al. (2019) investigated the bending properties of solid fir (Pseudotsuga menziesii Mirb.) beams reinforced with flax, GFRP, BFRP, and hybrid FRP. Their findings indicated that fiber-reinforced polymers enhanced the bending properties of wood materials.

Karaman (2021) investigated the bending moment resistance of T-type reinforced with basalt and glass woven fabric. Karaman and Yildirim (2021) investigated the bending moment resistance of L-shaped strengthened basalt and glass woven fabric. Kılınçarsalan and Türker (2023) reported that the ash beams are practically reinforced in a “U” shape from the outer part of the beam with the BFRP. Türker (2024) studied the glulam column-beam connection, which is combined with a wood notching connection, and is wrapped with the CFRP, GFRP, BFRP, and AFRP.

Regarding the tensile strength perpendicular to fibers, joints reinforced with the BFRP, GFRP, and PSM are not applied, and it is considered that there is a deficiency in the literature. The reinforcement with the BFRP, GFRP, and PSM reinforced joints in the structural lumber is a new research topic. This study aims to determine the performance of the tensile strength perpendicular to fibers of wooden unreinforced, reinforced BFRP, GFRP, and plaster mesh (PSM) using the polyvinyl acetate (PVAc-D4), and polyurethane (PUR-D4) adhesive cured under room temperature conditions.

EXPERIMENTAL

Materials

Beech wood (Fagus orientalis Lipsky), which is used widely in the wood construction industry, was used as the wooden material. The lumber pieces were selected randomly from Yenice-Karabuk timber merchants in Turkey (Fig. 1a). Careful attention was paid to the fact that the wood material used in experimental studies was not subjected to physical damage, mechanical impacts, or biological harm. It is a material with a full-dry density (D0) of 0.630 g/cm³ and, air-dry density (Dl2) of 0.660 g/cm³, and its tensile strength perpendicular to fibers (┴σt) is 7 N/mm² (Bozkurt and Erdin 2011).

Fig. 1. Materials used in experiments: a) Beech wood, b) PVAc-D4 adhesive, c) PUR-D4 adhesive, (d) GFRP, e) BFRP, and f) PSM

The polyvinyl acetate (PVAc-D4) was obtained from Kronen Furniture Glue Accessory Industrial Products Industry and Trade Limited Company in Turkey (Fig. 1b). The technical properties of the PVAc-D4 were as follows: density of 1.080 g/cm³, pH of 3.5 (25 °C), viscosity of 14.000 to 15000 mPa·s (25 °C), application amount of (200 gr/m²).

The polyurethane adhesive (PUR-D4) was obtained from Apel Kimya Industry and Trade Inc., in Turkey (Fig. 1c). The technical properties of the PUR-D4 were as follows: density of 1.110 g/cm³, pH of 5.0 (25 °C), viscosity of 5000 to 10000 mPas (20 °C), and application amount of (200 gr/m²).

The BFRP and GFRP for 200 gr/m² plain materials were obtained from Dost Chemical Industry Raw Material Industry and Trading Company in Turkey (Fig. 1d,e respectively). The BFRP and GFRP were prepared by cutting to 1000 mm in length and 52 mm in width. The density of BFRP and GFRP are 2.8 gr/cm³ and 2.56 gr/cm³, respectively.

The BFRP and GFRP values of elasticity modulus, tensile strength, and elongation to fracture were 8900 and 76000 MPa, 2800 and 2500 MPa, and 3.15% and 3.2%, respectively (Fiore et al. 2011) The PSM used weighed 160 g/m². It was alkali resistant and orange in color, with a 4 mm × 4 mm mesh pattern (Fig. 1e).

Preparation and Construction of Specimens

In the preparation of the test samples, the wooden materials were sawn using a high-speed circular saw machine to 3 mm thickness, 50 mm width and 1000 mm length, with the annual rings perpendicular to the adhesion surface (Fig. 2a). Once stacked, the slats were stored in a temperature-controlled room with a consistent temperature of 20 ± 2 °C and relative humidity conditions of 65 ± 5%. The slats remained in the specified environment until they attained a moisture content of 12%. The test samples were prepared following the guidelines outlined in the TS 5497 EN 408 (2006) standard. The PVAc-D4 and PUR-D4 adhesives were utilized in the preparation of the samples.

After the edges and surfaces of the wooden materials were smoothed in the planer machine (Fig. 2b), they were brought to the appropriate thickness (2.5 ± 0.1 mm) in the high-speed thicknessing machine, and the pressing process was started (Fig. 2c). For interlayer samples, one layer of reinforced materials (GFRP, BFRP, and PSM) was used for intermediate support between solid layers. Approximately 200 g/m² of adhesive was used for surface (Fig. 2d). The samples, which consisted of two layers, were placed into a hydraulic press (Hydraulic Veneer SSP-80; ASMETAL Wood Working Machinery Industry Inc., Ikitelli, Istanbul, Turkey) at room temperature. The press exerted a pressure of approximately 1.5 N/mm² on the samples for 3 h. As a result, the test samples were produced in cold pressure at 20 ± 2 °C and 65 ± 5% relative humidity. The pressing of test samples in the are shown in Fig. 2e.

After the pressing process, one of the edges was smoothed on the planer machine, and test samples were prepared on a high-speed circular saw machine in accordance with the TS ISO 13061-7 (2021) standards (Fig.3a,c). On the Vertical Drill Column Stand Lathe Drill machine, appropriate settings were made, and two holes of Ø25 mm and 50 ± 1 mm depth were opened in the middle of the test samples, symmetrically in the direction of the part thickness. Test samples were obtained by grading on a horizontal circle machine with plotter (Fig. 3b). Specimens under tensile test were fabricated in the form illustrated in Fig. 4. According to this, two adhesive types and three fiber-reinforced polymers (BFRP, GFRP, PSM, and control), and 10 samples of each material (2 x 4 x 10 =80) were the variables. A total of 80 specimens were constructed in this research. Before testing, all samples were conditioned in a humidity chamber controlled at 20 ± 2 °C and 65% relative humidity (RH) for two weeks.

Fig. 2. Production stages of test samples

Fig. 3. Manufacturing process for experimental samples: a) Slats, b) Hole drilling process, c) Test samples

Fig. 4. Geometry of specimens in the test (Unreinforced test samples, reinforced with BFRP, GFRP, and PSM test samples (dimensions in mm)

Mechanical Tensile Tests

For the tensile strength tests, the specimens were tested using an electromechanical universal testing machine (UTM), in the laboratory of Kütahya Dumlupınar University Simav Technical Education Faculty having a capacity of 10 kN, in which they were subjected to a tensile force perpendicular to the substrate wood fibers (Fig. 5). According to the TS ISO 13061-7 (2021) standard, the applied load increased monotonically, due to the crossbar displacement at a rate of 2 mm/min, until the joint rupture. The loading was continued until separation occurred on the surface of the test samples and from the observed load (F_max), and the bonding area of the sample (A), the tensile strength perpendicular to fibers (┴σt) was calculated using Eq. 1,

(1)

where ┴σt is the tensile strength perpendicular to fibers (N/mm²), F_max is the ultimate applied force (N), and A is the bonding area of the sample (mm²).

Fig. 5. Apparatus used to hold specimens for the tensile strength perpendicular to fibers tests.

Statistical Analysis

Statistical analysis (Statistical Software, a computer-based statistical package, Minitab, Minitab®18, State College, PA, USA) was performed to examine the data according to the analysis of variance (ANOVA) with the Duncan test (p < 0.05).

RESULTS AND DISCUSSION

The mean values ┴σt under tension of the experimental samples with their standard deviation and coefficients of variation are presented in Table 1.

Table 1. Mean Values of the ┴σt of Joints and Their Coefficients of Variation

SD: Standard deviation, COV: Coefficient of variation, No-SMT: Unreinforced samples, ┴σt: tensile strength perpendicular to fibers

According to Table 1, when interactions of the adhesive types, FRP types, and drilled types were compared, the highest ┴σt value was obtained for reinforced BFRP bonded with PUR-D4 adhesive in the undrilled samples (5.76 N/mm²). The lowest ┴σt value was obtained for reinforced PSM bonded with PVAc-D4 adhesive in the drilled samples (2.45 N/mm²). It can be said that BFRP, PU-D4 adhesive, and undrilled increase the ┴σt of the wood structural.

The results of the two-way ANOVA analysis of the adhesive types, and fiber-reinforced polymers on the tension strength perpendicular to fibers of the experimental samples under the tension load are given in Table 2.

According to the analysis of variance, as presented in Table 2, the effects of the main factors, including FRP types (B) and hole types (C), were found to be statistically significant. In contrast, adhesive types (A), two-way interactions of adhesive types × FRP types (A×B), and adhesive types × hole types were insignificant at the level of 0.05. Three-factor interactions of adhesive types × FRP types × hole types (A×B×C) were also statistically insignificant (p ≤ 0.05). Tukey test was carried out to determine these differences. The ┴σt mean according to the independent effects of test variables are given in Table 3.

Table 2. Summary of the ANOVA Results for ┴σt

df: Degrees of freedom, ^a Adhesive types (PVAc-D4, PUR-D4), ^bFRP types (BFRP, GFRP, and PSM), and ^cDrilled types (Undrilled, drilled)

Table 3. Independent Effects of Test Variables on Mean Values of ┴σt of Joints

┴σt: tensile strength perpendicular to fibers, HG: Homogeneity groups

When the comparison results of adhesive types were examined, it was seen that the highest ┴σt value was obtained for PUR-D4 (4.06 N/mm²). The ┴σt of PVAc-D4 adhesive was much lower (3.97 N/mm²). The PUR-D4 was 2.3% stronger than the PVAc-D4 (Table 3). The reason for this, the PUR-D4 was higher than the adhesion and cohesion power, tensile strength, and technological properties of the PVAc-D4 used in the experiments.

For the FRP types, the highest ┴σt value was obtained in BFRP (4.95 N/mm²), and the lowest was in the PSM (2.98 N/mm²). The ┴σt value according to reinforced FRP declined in the order to BFRP, GFRP, unreinforced, and PSM. The ┴σt value of samples reinforced with BFRP was 13%, 32%, and 66% higher than those reinforced with GFRP, unreinforced, and reinforced PSM, respectively.

In the literature, some studies reported that BFRP has higher tensile strength and modulus of elasticity than GFRP (Wei et al. 2010; Carmisciano et al. 2011; Lopresto et al. 2011; Dorigato and Pegoretti 2012).

For the drilled types, the highest ┴σt value was obtained in undrilled samples (4.60 N/mm²), and the lowest was in the drilled samples (3.44 N/mm²). Holes drilled into the test samples reduced the tensile strength of the wooden fibers.

Fig. 6. Product group comparisons according to the adhesive types, FRP types, and drilled types

Figure 6 shows a graphical representation of the effects of the selected monitored factors on the ┴σt of the experimental samples. The combined effect of the type of adhesive, type of the FRP, and the drilled selected type is shown for different cases. In the case of the ┴σt, reinforced BFRP bonded with PUR-D4 adhesive in the undrilled samples achieved an average of 145% higher values than reinforced PSM bonded with PVAc-D4 adhesive in the drilled samples.

Fiorelli and Alves (2003) reported that the increase in stiffness of timber beams strengthened with the GFRP was between 15% and 30%. Yang et al. (2008) reported that the ultimate bearing capacity of the FRP-reinforced beam exhibited an increase between 17.7% and 77.3% in comparison to the control beam. André and Johnsson (2010) reported that the maximum bending load of the specimen strengthened with GFRP was 23% higher than that of the specimen strengthened with FFRP. Borri et al. (2013) investigated the strengthening of low-grade and high-grade wood beams with flax and BFRP. The findings indicated an increase in bending strength of 38.6% and 65.8%, respectively. Zuo et al. (2015) reported that the bending behavior of BFRP-reinforced glulam beams was better compared to the unreinforced control beam, with the ultimate bending capacity, bending stiffness, and ductility coefficient increasing by 20.9% to 111%, 18.7% to 27.6%, and 23.0% to 74.3%, respectively. Basterra et al. (2017) conducted comparative experiments and reported that when the reinforcement ratio of GFRP sheet reinforced lumber beams was 1.07% and 1.6%, respectively, the mean stiffness increased 12.1% and 14.7%, respectively, and the bending capacity increased 23%. Monaldoa et al. (2019) explained that beams reinforced with BFRP have a bending ultimate load higher by about 20% than GFRP. Kılınçarslan and Türker (2023) determined that the flexural strength value of the reinforced beam increased 18% and the elasticity modulus value increased 25% compared to the reference beam.

In the ┴σt test, after the maximum load (F_max) of the test specimen against the applied force was reached, the end of the test varied with the toughness property of the test specimen. The load–deformation graphs obtained during the ┴σt tests are shown in Fig. 7. With FRP materials, after reaching the maximum load, the test sample suddenly ruptures, and the test is completed. Such materials are referred to as brittle materials. In some materials, after reaching the maximum load, the test sample breaks away from the adhesion surface slowly or gradually as the test is completed.

Fig. 7. Load–deformation graphs based on ┴σt test results

Failure Modes

The failure modes given in the study can be judged based on the images taken after the maximum load carrying capacity in the ┴σt test application. The failure modes of unreinforced and reinforced with BFRP, GFRP, and PSM beech samples are given in Fig. 8. It appears that there was no deformation in the beech wood. It has been observed that the tensile failures occurred on the adhesion surface and FRP materials in all experimental groups. In strengthened samples, the rupture was transferred to the glue layer between the layers. The failures were observed in the glue line and FRP materials in all test specimens. It was determined that the PSM+ PVAc-D4+ Hole test specimens had the highest failure.

The PSM+ PUR D4+ Hole, GFRP+PUR D4+Hole, Unreinforced+PVAc-D4+Hole, PSM+PVAc-D4, and Unreinforced+PUR D4+Hole test specimens followed respectively.

Fig. 8. Failure modes of the unreinforced and reinforced with FRP samples

CONCLUSIONS

The tensile strength perpendicular to fibers of the timber reinforced with basalt fiber-reinforced polymer (BFRP), glass fiber-reinforced polymer (GFRP), and plaster mesh (PSM) using PVAc-D4 and PUR-D4 adhesive was investigated in this study.

According to the overall results, the experimental samples reinforced with BFRP using PUR-D4 adhesive demonstrated the best properties among all the tested samples. However, it is important to note that the unreinforced samples using PVAc-D4 adhesive exhibited the lowest value among all samples.
On the empirical findings regarding the technical characteristics of BFRP as support materials and PUR-D4 as glue, the tensile strength perpendicular to fibers of the wood material was observed to be improved.
Given the substantial enhancements in the resistance properties of the intermediate filling material utilized in reinforced wood materials, it is advisable to prioritize high-strength properties in wood furniture and structural timber materials.

ACKNOWLEDGMENTS

The author declares that there are no funds and no conflict of interest.

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Article submitted: September 18, 2024; Peer review completed: October 19, 2024; Revised version received and accepted: October 24, 2024; Published: November 4, 2024.

DOI: 10.15376/biores.20.1.42-56